1. Field of the Invention
This invention generally relates to an optical recording medium formed with information-corresponding depressions or pits which are sensed by a laser light beam during the reproduction of information therefrom. This invention specifically relates to an optical recording medium which stores information with a security against an illegally reproducing process. This invention also relates to a method of fabricating an optical recording medium.
2. Description of the Prior Art
A general optical recording medium has a transparent substrate formed with small depressions or pits corresponding to stored information. During the reproduction of the information from the recording medium, the depressions or pits are sensed by a laser light beam. A typical example of such an optical recording medium is an optical disc. A CD-ROM (compact disc read-only memory) is one type of the optical disc.
An optical disc of a special type stores first information which can be reproduced by a commercially available device, and second information represented by a secret code which can not be reproduced by the commercially available device. The reproduction of the second information is permitted by using key information related to the secret code. In general, the second information represents document data, image data, or program software. On the other hand, the first information represents an epitome of the second information.
Such an optical disc is handled as follows. A customer can check the epitome of second information in an optical disc by reproducing and monitoring first information before buying the optical disc. After the buy of the optical disc, the customer is supplied with related key information by paying an additional fee.
Another known optical disc has a magnetic layer at a side opposite the optical read side. The magnetic layer generally stores information corresponding to a secret code. Since an optical head of a general reproducing device can not operate on the magnetic layer, a special reproducing device equipped with a magnetic head is required to handle such an optical disc.
Still another known optical disc is provided with a bar code at a label region or an outer edge region which Is not scanned by an optical head of a general reproducing device. Generally, the bar code is used as information related to a secret code. A special reproducing device provided with a bar-code reader is required to handle such an optical disc.